Titanium

Titanium is a lustrous, silver-grey metal combining low density (approximately 60% that of steel) with tensile strength comparable to many steel alloys, and exceptional corrosion resistance in virtually all environments. These properties make it the premier structural material for aerospace applications: aircraft airframes, jet engine compressor blades, and missile casings. Its production, however, is one of the most technically demanding and energy-intensive of any common metal. The Kroll process, the only commercially viable production route, reduces titanium tetrachloride with magnesium metal in an inert argon atmosphere at high temperature, producing a sponge-like titanium mass that must then be re-melted in a vacuum arc furnace. The process is batch-based, slow, and cannot be easily scaled, which is why titanium remains dramatically more expensive than its ore would suggest.